Carburetors and intake systems of gasoline engines as well as injection systems for fuel metering are increasingly being contaminated with impurities which are caused by dust particles from the air, and combustion hydrocarbon residues from the combustion chamber and the crank case vent gases passed into the carburetor.
These residues shift the air/fuel ratio during idling and in the lower part-load range so the mixture becomes leaner, the combustion becomes more incomplete and in turn the proportions of uncombusted or partly combusted hydrocarbons in the exhaust gas become larger and the gasoline consumption increases.
It is known that for avoiding these disadvantages, fuel additives are used for keeping valves and carburetors or intake systems of gasoline engines clean (cf. for example. M. Rossenbeck in Katalysatoren, Tenside, Mineralöladditive, Editors J. Falbe, U. Hasserodt, page 223, G. Thieme Verlag, Stuttgart 1978).
A distinction is now made between two generations depending on the mode of action as well as on the preferred place of action of such detergent additives.
The first additive generation could only prevent the formation of deposits in the intake system but could not remove deposits already present, whereas the modern additives of the second generation can do both (keep-clean and clean-up effect) and can do so in particular owing to their excellent thermal stability in zones of relatively high temperature, i.e. in the intake valves. Such detergents, which may originate from a large number of classes of chemical substances, for example polyalkeneamines, polyetheramines, polybutene Mannich bases or polybutene-succinimides, are generally used in combination with carrier oils and in some cases further additive components, e.g. corrosion inhibitors and demulsifiers. The carrier oils perform a solvent or wash function in combination with the detergents. Carrier oils are as a rule high-boiling, viscous, heat-stable liquids which coat the hot metal surface and thus prevent the formation or deposition of impurities on the metal surface.
Such formulations of detergents with carrier oils can be classified in principle as follows (depending on the type of carrier oils or carrier oil):    a) mineral-oil based (i.e. only mineral oil-based (mineral) carrier oils are used)    b) fully synthetic (i.e. only synthetic carrier oils are used) or, to a minor extent,    c) semisynthetic (i.e. mixtures of mineral oil-based and synthetic carrier oils are used).
It is known from the prior art that additive formulations thus described are used in gasoline fuels. It is true in general that fully synthetic additive packets have better keep-clean properties than mineral oil-based ones. It is also generally true that such fully synthetic additive packets have lower viscosities, especially at lower temperatures, than mineral oil-based formulations. Fully synthetic detergent additive packets to date thus have substantial advantages since, in addition to having good keep-clean properties with respect to the intake system, they can be more readily handled and processed, especially at relatively low temperatures.
In the classes consisting of the pure mineral oil-based and semisynthetic formulations, there is a need for optimization compared with the abovementioned fully synthetic additive packets.